The present invention relates to a vibrating membrane fluid circulator.
Numerous types of pump are known both in industrial and in biomedical fields. The following can be mentioned:
reciprocating positive displacement pumps whose main elements are pistons or membranes associated with admission and delivery valves. Their main drawback lies in the cyclical aspect of their motion and in the presence of the valves;
so-called xe2x80x9cperistalticxe2x80x9d positive displacement pumps in which continuously moving wheels deform and compress a flexible tubular pump body. The compression can be damaging for certain liquids to be pumped that include sensitive elements (e.g. blood);
xe2x80x9cimpellerxe2x80x9d pumps such as centrifugal pumps based on a vaned rotor or a vortex. Their drawback lies in the high speed of rotation which generates shear in the fluid streams, friction, and cavitation, all of which phenomena can be damaging to fragile fluids; and
axial turbine pumps in which fragile fluids suffer likewise from the same drawbacks as in the preceding pumps.
Also known is a vibrating-membrane fluid propulsion device, as described in document FR-A-2 650 862. That device provides a technical solution which is not always suitable for obtaining the hydraulic performance required by most industrial and biomedical applications,
The vibrating membrane fluid circulator of the invention proposes solutions whereby the fields of application of the circulator are enlarged, the hydraulic performance thereof is improved, the circulator is more compact, and finally the pump body can he for a single use only, which is advantageous in the biomedical field.
To this end, the fluid circulator of the invention comprises an internal hydraulic circuit made up in succession of an admission orifice, a pump body and a delivery orifice, the pump body having two rigid walls defining therebetween a pumping chamber for the fluid extending from said admission orifice to said delivery orifice with a deformable membrane located in said pumping chamber and having two external surfaces facing respectively said walls, at least one of said membrane surfaces and at least one said walls defining in said pumping chamber a circulation space for the fluid, said deformable membrane being maintained under a tension parallel to the fluid circulation direction from said admission orifice to said delivery orifice, said membrane having one edge located near said admission orifice and provided with means for coupling to a motor member generating a periodic excitation force substantially normal to the external faces of said membrane, said circulation space having a cross section perpendicular to the fluid circulation direction the size of which measured in the periodic force direction being progressively decreasing from said admission orifice to said delivery orifice.
Means to keep the membrane under tension enable it to constitute a medium for waves travelling from the edge of the membrane subjected to the excitation force towards its opposite edge. Displacement of these waves is accompanied by forced damping due to the shape of the rigid walls, which results in a reduction of the width (thickness) of the cross section of the circulation space along the circulation direction, so that mechanical energy is transferred from the membrane to the fluid, with this appearing in the form of a pressure gradient and of a fluid flow. The characteristics of the pressure gradient and of the fluid flow are related to the dimensions of the pump body, to the dimensions of the membrane, to the shape and the spacing of the rigid walls, to the mechanical characteristics and the tension state of the membrane, and to the parameters of the excitation applied thereto.
The periodic excitation of the membrane is implemented at frequencies which are associated with the mechanical characteristics of the membrane and with its tension state. The excitation frequency should be kept down to low values of the order of 40 Hz to 80 Hz so as to avoid localized pressure effects and shear effects between fluid streams.
In one embodiment of the invention, said pumping chamber is a flat tubular chamber and the membrane is a flat membrane tapered towards the edge thereof located near said delivery orifice.
In another embodiment of the invention, said pumping chamber is an annular tubular chamber and the membrane is shaped as a sleeve with a larger thickness at its edge near said admission orifice than at its edge near said delivery orifice.
Other characteristics and advantages appear from the description given below of various embodiments of the invention.